The HER2 (ErbB2) receptor tyrosine is a member of the epidermal growth factor receptor (EGFR) family of transmembrane receptors. Overexpression of HER2 is observed in approximately 20% of human breast cancers and is implicated in the aggressive growth and poor clinical outcomes associated with these tumors (Slamon et al (1987) Science 235:177-182).
Trastuzumab (CAS 180288-69-1, HERCEPTIN®, huMAb4D5-8, rhuMAb HER2, Genentech) is a recombinant DNA-derived humanized, IgG1 kappa, monoclonal antibody version of the murine HER2 antibody which selectively binds with high affinity in a cell-based assay (Kd=5 nM) to the extracellular domain of the human epidermal growth factor receptor2 protein, HER2 (ErbB2) (U.S. Pat. No. 5,677,171; U.S. Pat. No. 5,821,337; U.S. Pat. No. 6,054,297; U.S. Pat. No. 6,165,464; U.S. Pat. No. 6,339,142; U.S. Pat. No. 6,407,213; U.S. Pat. No. 6,639,055; U.S. Pat. No. 6,719,971; U.S. Pat. No. 6,800,738; U.S. Pat. No. 7,074,404; Coussens et al (1985) Science 230:1132-9; Slamon et al (1989) Science 244:707-12; Slamon et al (2001) New Engl. J. Med. 344:783-792). Trastuzumab contains human framework regions with the complementarity-determining regions of a murine antibody (4D5) that binds to HER2. Trastuzumab binds to the HER2 antigen and thus inhibits the growth of cancerous cells. Trastuzumab has been shown, in both in vitro assays and in animals, to inhibit the proliferation of human tumor cells that overexpress HER2 (Hudziak et al (1989) Mol Cell Biol 9:1165-72; Lewis et al (1993) Cancer Immunol Immunother; 37:255-63; Baselga et al (1998) Cancer Res. 58:2825-2831). Trastuzumab is a mediator of antibody-dependent cellular cytotoxicity, ADCC (Lewis et al (1993) Cancer Immunol Immunother 37(4):255-263; Hotaling et al (1996) [abstract]. Proc. Annual Meeting Am Assoc Cancer Res; 37:471; Pegram M D, et al (1997) [abstract]. Proc Am Assoc Cancer Res; 38:602; Sliwkowski et al (1999) Seminars in Oncology 26(4), Suppl 12:60-70; Yarden Y. and Sliwkowski, M. (2001) Nature Reviews Molecular Cell Biology, Macmillan Magazines, Ltd., Vol. 2:127-137).
HERCEPTIN® was approved in 1998 for the treatment of patients with ErbB2-overexpressing metastatic breast cancers (Baselga et al, (1996) J. Clin. Oncol. 14:737-744) that have received extensive prior anti-cancer therapy, and has since been used in over 300,000 patients (Slamon D J, et al. N Engl J Med 2001; 344:783-92; Vogel C L, et al. J Clin Oncol 2002; 20:719-26; Marty M, et al. J Clin Oncol 2005; 23:4265-74; Romond E H, et al. T N Engl J Med 2005; 353:1673-84; Piccart-Gebhart M J, et al. N Engl J Med 2005; 353:1659-72; Slamon D, et al. [abstract]. Breast Cancer Res Treat 2006, 100 (Suppl 1): 52). In 2006, the FDA approved HERCEPTIN® (trastuzumab, Genentech Inc.) as part of a treatment regimen containing doxorubicin, cyclophosphamide and paclitaxel for the adjuvant treatment of patients with HER2-positive, node-positive breast cancer. While the development of HERCEPTIN® provided patients with HER2-positive tumors a markedly better outcome than with chemotherapy alone, virtually all HER2-positive, metastatic breast cancer (MBC) patients will eventually progress on available therapies. Opportunities remain to improve outcomes for patients with MBC. Despite trastuzumab's diverse mechanisms of action, a number of patients treated with trastuzumab show either no response or stop responding after a period of treatment benefit. Some HER2+ (HER2 positive) tumors fail to respond to HERCEPTIN® and the majority of patients whose tumors respond eventually progress. There is a significant clinical need for developing further HER2-directed cancer therapies for patients with HER2-overexpressing tumors or other diseases associated with HER2 expression that do not respond, or respond poorly, to HERCEPTIN® treatment.
An alternative approach to antibody-targeted therapy is to utilize antibodies for delivery of cytotoxic drugs specifically to antigen-expressing cancer cells. Maytansinoids, derivatives of the anti-mitotic drug maytansine, bind to microtubules in a manner similar to vinca alkaloid drugs (Issell B F et al (1978) Cancer Treat. Rev. 5:199-207; Cabanillas F et al. (1979) Cancer Treat Rep, 63:507-9. Antibody-drug conjugates (ADCs) composed of the maytansinoid DM1 linked to trastuzumab show potent anti-tumor activity in HER2-overexpressing trastuzumab-sensitive and trastuzumab-resistant tumor cell lines, and xenograft models of human breast cancer. A conjugate of maytansinoids linked to the anti-HER2 murine breast cancer antibody TA.1 via the MCC linker was 200-fold less potent than the corresponding conjugate with a disulfide linker (Chari et al (1992) Cancer Res. 127-133). Antibody-drug conjugates (ADCs) composed of the maytansinoid, DM1, linked to trastuzumab show potent anti-tumor activity in HER2-overexpressing trastuzumab-sensitive and -resistant tumor cell lines and xenograft models of human cancer. Trastuzumab-MCC-DM1 (T-DM1) is currently undergoing evaluation in phase II clinical trials in patients whose disease is refractory to HER2-directed therapies (Beeram et al (2007) “A phase I study of trastuzumab-MCC-DM1 (T-DM1), a first-in-class HER2 antibody-drug conjugate (ADC), in patients (pts) with HER2+ metastatic breast cancer (BC)”, American Society of Clinical Oncology 43rd:June 2 (Abs 1042; Krop et al, European Cancer Conference ECCO, Poster 2118, Sep. 23-27, 2007, Barcelona; U.S. Pat. No. 7,097,840; US 2005/0276812; US 2005/0166993).
Combination therapy in which two or more drugs are used together in some dosing regimen or administration form, typically has one or more goals of: (i) reducing the frequency at which acquired resistance arises by combining drugs with minimal cross-resistance, (ii) lowering the doses of drugs with non-overlapping toxicity and similar therapeutic profile so as to achieve efficacy with fewer side effects, i.e. increase therapeutic index, (iii) sensitizing cells to the action of one drug through use of another drug, such as altering cell-cycle stage or growth properties, and (iv) achieving enhanced potency by exploiting additivity, or greater than additivity, effects in the biological activity of two drugs (Pegram, M., et al (1999) Oncogene 18:2241-2251; Konecny, G., et al (2001) Breast Cancer Res. and Treatment 67:223-233; Pegram, M., et al (2004) J. of the Nat. Cancer Inst. 96(10):739-749; Fitzgerald et al (2006) Nature Chem. Biol. 2(9):458-466; Borisy et al (2003) Proc. Natl. Acad. Sci. 100(13):7977-7982).
Loewe additivity (Chou, T. C. and Talalay, P. (1977) J. Biol. Chem. 252:6438-6442; Chou, T. C. and Talalay, P. (1984) Adv. Enzyme Regul. 22:27-55; Berenbaum, M. C. (1989) Pharmacol. Rev. 41:93-141) and Bliss independence/synergy (Bliss, C. I. (1956) Bacteriol. Rev. 20:243-258; Greco et al (1995) Pharmacol. Rev. 47:331-385) are methods used for calculating the expected dose-response relationship for combination therapy compared to monotherapy based on parameters such as IC50, the dose of drug needed to achieve 50% target inhibition and equal to Ki in the simplest case.
HER2 dimerization inhibitor antibodies and EGFR inhibitors have been reported for combination therapy against cancer (US 2007/0020261). Trastuzumab-MCC-DM1 (T-DM1) and pertuzumab have individually demonstrated activity in MBC patients, and a combination of pertuzumab and trastuzumab has been shown to be active in HER-positive MBC patients (Baselga J, et al. “A Phase II trial of trastuzumab and pertuzumab in patients with HER2-positive metastatic breast cancer that had progressed during trastuzumab therapy: full response data”, European Society of Medical Oncology, Stockholm, Sweden, Sep. 12-16, 2008).